There is a large body of work that suggest that local environment around the chromophore may affect its fluorescence lifetime. Variation in pH [1]}, viscosity [2]}, temperature [3]} and pressure [4]} have been shown to have an effect on the fluorescence lifetime of different fluorophores. Although, viscosity of the solvent does seem to affect the fluorescence lifetime, there is no correlation between the viscosity and the fluorescence lifetime of GFP [2]}. Dependence of fluorescence lifetime on refractive index of the solvent has been investigated by Suhling et. al. [6]}. These authors find that the inverse of the fluorescence lifetime scales linearly with square of the refractive index for GFP [6]}, [8]}, [9]} and Enhanced Cyan and Yellow Fluorescent Protein [10]}. At a given temperature, the refractive index of water increases with increasing pressure [11]}. However, these changes in refractive index would only lead to decrease in fluorescence lifetime.
